As a type of vehicle using an engine as a drive source, vehicles equipped with an attenuation mechanism have been known so far. For example, Japan Laid-open Patent Application Publication No. 2007-320494 describes a practical example that a dynamic damper is provided for inhibiting resonance caused by vibration of a drive source.
In electric cars or high-power hybrid cars, a motor has a large inertia, whereby chances are that intense torque fluctuations occur due to input from drive wheels in traveling a winding road or in escaping from a low-μ road. There is a risk that a drive system is damaged or broken by the intense torque fluctuations. Hence, it is required to inhibit the intense torque fluctuations. For example, attaching a dynamic damper, a torque limiter or so forth is a countermeasure assumable as means for inhibiting the intense torque fluctuations.
However, in attachment of the dynamic damper as a countermeasure, a large torsion angle is required because a frequency inputted from a winding road is low in general, whereby it is concerned that the entire device is excessively increased in size. On the other hand, in attachment of the torque limiter as a countermeasure, a transmission torque is required to be greater than or equal to a drive torque, whereby it is concerned as well that the entire device is excessively increased in size. Thus, these countermeasures have a drawback that increase in size of the entire device inevitably results in increase in installation space.
In view of the above, it is an object of the present invention to provide a power transmission system and an attenuation mechanism, both of which can inhibit intense fluctuations in torque inputted thereto from a drive wheel without increasing an installation space.